Theoretical study on peculiar structural transition and superconductivity of elements under high pressures

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For calcium we have succeeded in predicting new high pressure phases V and VI, and also in clarifying that the phase III with simple cubic structure thermodynamically stabilizes at the temperatures of 10-300 K. For gold, we have predicted that the fcc structure with ABC stacking of the close-packed layer transforms into the ABCACB stacking structure at around 400 GPa. By applying our first-principles genetic algorithm code we have succeeded in identifying the crystal structures of phases V and VI of yttrium. As for superconductivity of gold and its alloys we have shown that the superconducting transition temperature TC of pure gold is quite low (～0.04 μK), but by alloying gold with indium TC dramatically increases to 0.1K for Au_<0.875>In_<0.125>.